British Columbia cities have some of the cleanest air on earth, according to the World Health Organization, which collected air quality data from over a thousand cities around the world.

The global health body released its list of measurements ranking 1,100 cities in 91 countries this week and B.C. had six of the top 10 cities in the world, including Kitimat, Burns Lake, Houston, Terrace, Nanaimo and Nelson.

The city with the cleanest air in the world was Whitehorse in the Yukon. The worst was Ulaanbaatar, the capital of Mongolia.

David Reid works for the EcoSociety in Nelson. He says geography plays a role, as do trees.

"In the big picture we're lucky to have the air quality we have," he said.

But Reid says regulations and personal choice are also helping.

"I think regulation is a big part of it. And we as individuals are becoming more conscious of air quality in driving and consumption choice," said Reid.

"We certainly have air quality issues, such as old woodstoves and idling cars," he said.

Small particles a health risk

The list is intended to highlight the need to reduce outdoor air pollution, which is estimated to cause 1.34 million premature deaths each year.

The study focused on the prevalence of PM10 particles, which are particles of 10 micrometers or less that can penetrate the lungs and may enter the bloodstream.

The tiny particles can cause respiratory problems and other diseases in humans, including heart disease, lung cancer and asthma.

Most countries that ranked well benefit from lower population density, favourable climates and stricter air pollution regulation — conditions unavailable to those at the bottom of the list.

"Across the world, city air is often thick with exhaust fumes, factory smoke or soot from coal-burning power plants. In many countries there are no air quality regulations and, where they do exist, national standards and their enforcement vary markedly," Dr. Maria Neira, WHO Director for Public Health and Environment, said in a release.

The organization said investments to lower pollution levels quickly pay off due to lower disease rates and health-care costs.